1. Field of the Invention
The present invention relates to an oil seal, and in particular to a two-liquid-sealing oil seal in which liquid present on both sides of the oil seal are sealed.
2. Description of Related Art
Conventionally known oil seals include a one-liquid-sealing oil seal having a single lip for preventing lubrication oil around a rotary shaft from leaking from one side to the other side of the oil seal, and a two-liquid-sealing oil seal having lips provided on both sides of the oil seal for preventing lubrication oils present on both sides from leaking from one side to the other side or vise versa. The two-liquid-sealing oil seal is provided, for example, between the outer circumference of a crank shaft of an engine and the inner circumference of a flywheel housing in order to seal engine oil fed on the crank shaft and lubrication oil fed on a clutch disc on the flywheel side or a transmission.
The two-liquid-sealing oil seal includes an axial seal in which a lip is abutted on a circular metal ring fixed on the outer circumference of the rotary shaft to seal lubrication oil (for instance, see JP2002-250449A, on page 3 and FIG. 1). The metal ring with a substantially L-shaped cross section includes a cylinder fixed on the outer circumference of the rotary shaft and a flange continuously extending outward in the radial direction of the rotary shaft from the cylinder. The lubrication oil at one side is sealed by the axial seal lip abutted on the flange of the metal ring form the axial direction. Further, the lubrication oil at the other side is sealed by a radial seal lip abutted on the cylinder from the radial direction.
The above oil seal spatters the lubrication oil adhered on the metal ring by the centrifugal force due to the rotation of the metal ring with the rotary shaft. When the lubrication oil enters over the flange of the metal ring, the axial seal lip prevents further invasion of the lubrication oil. Since the almost all of the lubrication oil can be prevented form entering by the centrifugal force of the metal ring, the surface pressure of the axial seal lip against the metal ring can be set low. The axial seal prevents extraordinary abrasion at the high-rotation whereas is effective while the rotary shaft rotating at high speeds, and accordingly, the improvement of durability is desired.
Incidentally, as the material of the oil seal, a fluorocarbon rubber, a silicone rubber, a nitric rubber or the like is used. However, since the oil seal is used making contact with a rotary shaft, it is likely to wear on account of a use condition including a rotational speed and a temperature, and accordingly, the development of a material which is excellent in wear-resistance is desired. Particularly, since the radial seal lip abutted from the radial direction of the rotary shaft needs the surface pressure in some measure against the rotary shaft for preferably sealing around the rotary shaft, it is likely to wear with use for a long time. Accordingly, the improvement of durability and the long-lasting sealability have been desired.